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Michael Bates, Ross Tulloch, John Marshall, and Raffaele Ferrari

the effects of suppression. While these approaches are more in line with our work, the statistical uncertainty at long lags remains an issue in the estimation of suppression. While the use of tracer-derived diffusivities have their own associated uncertainty and drawbacks, given that our paper focuses on suppression of mixing over the entire globe, we prefer to compare our results against the surface diffusivity map of Abernathey and Marshall (2013 , shown in Fig. 1 ). Our goal is to rationalize

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F. Sévellec, A. C. Naveira Garabato, J. A. Brearley, and K. L. Sheen

circulation of global significance ( Rintoul and Naveira Garabato 2013 ). This view of the Southern Ocean stems from simple theoretical models of the regional circulation ( Olbers et al. 2004 ) and is found to hold in general circulation models of varying degrees of idealization and eddy-permitting capability ( Abernathey et al. 2011 ; Hallberg and Gnanadesikan 2006 ; Farneti and Delworth 2010 ). Nonetheless, the weakness and wide spatial distribution of the vertical flows associated with these

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J. H. LaCasce, R. Ferrari, J. Marshall, R. Tulloch, D. Balwada, and K. Speer

; Lumpkin and Pazos 2007 ; Sallée et al. 2008 ). These analyses suggest large regional variations. In the boundary currents (in the Agulhas and Brazil Currents and near the Kerguelen and Campbell Plateaus), diffusivities can reach values of 10 4 m 2 s −1 . In more quiescent regions, the diffusivities can be two orders of magnitude smaller. The DIMES floats were deployed in one such region (although they later entered the Drake Passage where they experienced much more rapid spreading). The dispersion

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Ross Tulloch, Raffaele Ferrari, Oliver Jahn, Andreas Klocker, Joseph LaCasce, James R. Ledwell, John Marshall, Marie-Jose Messias, Kevin Speer, and Andrew Watson

regional setup of the Massachusetts Institute of Technology general circulation model (MITgcm; Marshall et al. 1997a , b ), hereinafter referred to as the “Drake Patch.” The model’s horizontal grid resolution is one-twentieth of a degree (a resolution of 3 km × 6 km at the location of the tracer injection), spanning the Drake Passage from 75° to 35°S in latitude and from 160° to 20°W in longitude. The vertical mesh grid is divided into 100 layers of unequal thickness such that the top 70 layers, which

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Ru Chen, Sarah T. Gille, Julie L. McClean, Glenn R. Flierl, and Alexa Griesel

Tulloch et al. (2014) estimated meridional isopycnal diffusivities, using tracer and float observations collected during the DIMES experiment. Given the quasi-zonal orientation of the ACC west of the Drake Passage, their meridional diffusivities are expected to be approximately equivalent to cross-stream diffusivities. They extrapolated the vertical structures of the meridional diffusivities from the DIMES observations using a regional eddying model. However, their estimates do not resolve horizontal

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Dhruv Balwada, Kevin G. Speer, Joseph H. LaCasce, W. Brechner Owens, John Marshall, and Raffaele Ferrari

were deployed as part of the DIMES experiment, primarily between the synoptically observed positions of the Subantarctic Front (SAF) and Polar Front (PF) at 105°W. Additional floats were deployed downstream of this deployment site to supplement the dataset. The total number of floats deployed was 210. However, after failures, 140 float tracks comprising 183 years of float data (66 795 float days) were retrieved. Figure 1 shows a summary of the experimental design and regional geography, together

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J. Alexander Brearley, Katy L. Sheen, Alberto C. Naveira Garabato, David A. Smeed, and Stephanie Waterman

enhanced turbulent kinetic energy (TKE) dissipation. The theory of lee waves, initially developed by Bell (1975) , has recently been generalized from two- to one-dimensional topography and modified to account for saturation of the energy radiation flux at steep topography ( Nikurashin and Ferrari 2010a ). Coarse-scale regional and global estimates of lee-wave energy radiation ( Nikurashin and Ferrari 2010b ; Scott et al. 2011 ) are now available. Alongside the development of modified linear lee

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